/*
   Copyright The containerd Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.

   You may obtain a copy of the License at
       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package fifo

import (
	"fmt"
	"os"
	"sync"
	"syscall"

	"github.com/pkg/errors"
)

const oPathFlags = 0o10000000

type handle struct {
	f         *os.File
	fd        uintptr
	dev       uint64
	ino       uint64
	closeOnce sync.Once
	name      string
}

func getHandle(fn string) (*handle, error) {
	f, err := os.OpenFile(fn, oPathFlags, 0)
	if err != nil {
		return nil, errors.Wrapf(err, "failed to open %v with oPathFlags", fn)
	}

	var (
		stat syscall.Stat_t
		fd   = f.Fd()
	)
	if err := syscall.Fstat(int(fd), &stat); err != nil {
		f.Close()
		return nil, errors.Wrapf(err, "failed to stat handle %v", fd)
	}

	h := &handle{
		f:    f,
		name: fn,
		dev:  stat.Dev,
		ino:  stat.Ino,
		fd:   fd,
	}

	// check /proc just in case
	if _, err := os.Stat(h.procPath()); err != nil {
		f.Close()
		return nil, errors.Wrapf(err, "couldn't stat %v", h.procPath())
	}

	return h, nil
}

func (h *handle) procPath() string {
	return fmt.Sprintf("/proc/self/fd/%d", h.fd)
}

func (h *handle) Name() string {
	return h.name
}

func (h *handle) Path() (string, error) {
	var stat syscall.Stat_t
	if err := syscall.Stat(h.procPath(), &stat); err != nil {
		return "", errors.Wrapf(err, "path %v could not be statted", h.procPath())
	}
	if stat.Dev != h.dev || stat.Ino != h.ino {
		return "", errors.Errorf("failed to verify handle %v/%v %v/%v", stat.Dev, h.dev, stat.Ino, h.ino)
	}
	return h.procPath(), nil
}

func (h *handle) Close() error {
	h.closeOnce.Do(func() {
		h.f.Close()
	})
	return nil
}
